Technical Abstract:
Large-scale vegetable production frequently uses plastic mulch (polyethylene) to control weeds, maintain soil moisture, and raise soil temperature. Runoff and sediment loss from vegetables grown on plastic mulch has been shown to be an order of magnitude higher than from those grown in organic mulches. Laboratory studies were conducted to examine pesticide sorption characteristics and runoff losses from polyethylene. Glyphosate, chlorthalonil, endosulfan, es-fenvalerate and copper hydroxide were applied to polyethylene covered panels and maintained in a temperature controlled greenhouse. No significant difference was observed in the total glyphosate load detected in the runoff collected on days 1,3 and 7: ca. 65% of the applied glyphosate was removed form the plastic mulch on each day. In contrast, total load in runoff from panels treated with hydrophobic, semi-volatile pesticides were much less and decreased with time. Rainfall intensity can also affect pesticide concentration in the runoff. These data suggest that hydrophobicity and volatility need to be considered in determining pesticide fate on plastic mulch. Further pesticide fate predictions involving polyethylene using soil sorption and fate parameters to polyethylene are not always indicative of observed results.